A battery pack consists of one or more electrochemical cells or batteries, wherein each cell typically includes a positive electrode, a negative electrode, and an electrolyte or other material for facilitating movement of ionic charge carriers between the negative electrode and positive electrode. As the cell is charged, cations migrate from the positive electrode to the electrolyte and, concurrently, from the electrolyte to the negative electrode. During discharge, cations migrate from the negative electrode to the electrolyte and, concurrently, from the electrolyte to the positive electrode.
By way of example and generally speaking, lithium ion batteries are prepared from one or more lithium ion electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include, at least, a negative electrode, a positive electrode, and an electrolyte for facilitating movement of ionic charge carriers between the negative and positive electrode. As the cell is charged, lithium ions are transferred from the positive electrode to the electrolyte and, concurrently from the electrolyte to the negative electrode. During discharge, the lithium ions are transferred from the negative electrode to the electrolyte and, concurrently from the electrolyte back to the positive electrode. Thus with each charge/discharge cycle the lithium ions are transported between the electrodes. Such lithium ion batteries are called rechargeable lithium ion batteries or rocking chair batteries.
The electrodes of such batteries generally include an electroactive material having a crystal lattice structure or framework from which ions, such as lithium ions, can be extracted and subsequently reinserted and/or from which ions such as lithium ions can be inserted or intercalated and subsequently extracted. Recently a class of transition metal phosphates and mixed metal phosphates have been developed, which have such a crystal lattice structure. These transition metal phosphates are insertion based compounds and allow great flexibility in the design of lithium ion batteries.
A class of such materials is disclosed in U.S. Pat. No. 6,528,033 B1 (Barker et al.). The compounds therein are of the general formula LiaMIbMIIc(PO4)d wherein MI and MII are the same or different. MI is a metal selected from the group consisting of Fe, Co, Ni, Mn, Cu, V, Sn, Cr and mixtures thereof. MII is optionally present, but when present is a metal selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be and mixtures thereof. More specific examples of such compounds include compounds wherein MI is vanadium and more specifically includes Li3V2(PO4)3. U.S. Pat. No. 6,645,452 B1 (Barker et al.) further discloses electroactive vanadium phosphates such as LiVPO4F and LiV0.9Alo.1PO4F.
Although these compounds find use as electrochemically active materials these materials are not always economical to produce. Thus it would be beneficial to have a process for preparing such intercalation materials at lower temperatures and with faster reaction kinetics. The inventors of the present invention have now found a method for preparing a novel VPO4 precursor and a novel V—P—O/C precursor and processes employing such precursors to produce vanadium phosphate compounds more economically and efficiently.